3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, supports a multi-antenna transmission technology, in which a base station directs a beam toward a specific user terminal while directing a null toward another user terminal (see, for example, Non Patent Document 1).
In order to realize such a multi-antenna transmission technology using an FDD scheme, each of a plurality of user terminals feeds back precoder matrix information, which indicates a precoder matrix preferred to be used in a downlink, to a base station.
The base station precodes a downlink signal using the precoder matrix based on the precoder matrix information fed back from each user terminal. Then, the base station transmits the precoded downlink signal through a plurality of antenna ports (a plurality of feeding points). The precoder matrix includes a plurality of precoder matrix elements (a plurality of weights) corresponding to the plurality of antenna ports.